Relay automatic telephone system



Dec. 2, 1947. J. H. voss RELAY AUTOMATIC TELEPHONE SYSTEM Filed Dec. 12, 1945 l0 Sheets-Sheet 1 TO RINGING INTERRUPTER GEN. ST.

IN VEN TOR. JOHN H V08 5 ATTOR N EY Dec 2 1947.

J. H. VOSS RELAY AUTOMATIC TELEPHONE SYS TEM Filed Dec. 12, 1945 10 Sheets-Sheet 2 248 DIAL TONE FIG. 2

INVENTOR. JOHN H. VOSS ATTORNEY Dec. 2, '1947.

J. H. VOSS RELAY AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Sheet 3 Fil ed Dec. 12, 1945 INVENTOR. JOHN H. voss BY 5 ii ATTORNEY Dec. 2, 1947. J. voss 2,431,350

RELAY AUTOMATIC TELEPHONE SYSTEM Filed Dec. 12; 1945 10 Sheebs- -She et 4 FIG.4 I 42% INVENTOR. JOHN H. voss ATTORNEY Dc. 2, 1947. J. H. voss 2,431,850

RELAY AUTOMATIC TELEPHONE SYSTEM Filed Dec. 12, 1945 10 Sheets-Sheet 5 GRP. T50

JOHN V055 ATTORNEY Dec. 2, 1947. J. H. voss 2,431,850

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Dec. 2, 1947. I J, H, voss 2,431,850

RELAY AUTOMATIC TELEPHONE SYSTEM Filed Dec. 12, 1945 10 Sheets-Sheet 8 z' 0x F158 :52 a r 3 r '5 E 25 8 N n m w 8 8 8 8 3 8 m QN n .IO w m INVENTOR. I JOHN H. voss .ATTORNEY Dec. 2, 1947. J. H. voss' RELAY AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Shgt 10 Filed Dec. 12, 1945 mdE V u h. 10..

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INVENTOR. JOHN H. VOSS ATTORNEY Patented Dec. 2, 1947 UNITED STATES PATENT OFFICE RELAY AUTOMATifiZiiEPHdNE SYSTEM John H. Voss, Downers Grove,- 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application December 12, 1945, Serial No. 634,555

19 Claims. 1

The present invention relates in general to telephone systems, but more particularly to small community automatic exchanges or C. A. Xs of the all relay type, generally similar to that described in Patent No. 2,333,039, issued October 26 1943, to Edward S, Peterson.

An automatic telephone system of this type must be low in cost, and yet must provide most of the services provided with a larger system, plus some additional. It usually has a capacity of less than 200 lines, and should be sufliciently flexibleto permit adding or changing lines or services with a minimum of disturbance. For reasons of economy, many of the lines in such a system will be multi-party lines,v and as likely as, not, code ringing will be employed for signalling, particularly with the smaller switchboards'.

Such an exchange will usually not have. any toll operator; but must provide means whereby any subscriber can get access to an idle trunk leading to atoll operator at some nearby eX- change, easily and quickly. Means must also be provided whereby a special subscriber, Or a, local or distant operator, may have easy access to groups of direct trunks to certain other exchanges. Provision must also often be made for additional trunk groups leading to one or more private branch exchanges or P. B. X5, in the community;

It is the main object of the present invention to provide improved means for automatically selecting idle toll, inter-office or P. B. X trunks in an all relay system of the character described, without any sacrifice of speed, convenience or flexibility. Speed is obtained by the pre-s'election of idle trunks, in all cases. Convenience is achieved through the use of single-digit call numbers for all toll and. inter-office trunks, with four-digit call numbers used in. all other cases. Finally, flexibility is obtained through provisions permitting the assignment of trunks and subscribers lines to any tens group, under'normal circumstances.

Another object of the invention is. to provide separate points of access for light tralfic and heavy trafiic trunk groups, thereby to permit calls to both classes of trunk to proceed simultaneously, and independently of each other...

A; further object of the invention is to provide a separate point of access for P. B. X trunks, so as to permit calls to such trunks to proceed simultaneously with calls to other classes of trunks, without delay or interference between them.

Still another object of the invention is to pro vide means whereby two trunk groups may be 2. assigned in the same tens roup, thus avoiding in certain cases, the use of more tens relaysthan are actually required, in the'l iri-ks.

Other objects and features of the invention will be apparent from the specification and claims following, considered in conjunction with the accompanying drawings com-prising Figs. 1 to- 11 which show one embodiment of the invention as applied to a 1 00 line all relay system of the type described. Itshould be understood that the ar rangenient illustrated is merely one embodiment oi'the invention and not-necessarily the preferred embodiment, and that numerous modifications and rearrangements thereof are possible, with out departing from the spirit or scope of the invention as disclosed,

Referring to the drawings; Figs. 1 to 5 inclusive, when arranged as indicated in Fig. 11, with adjoining lines abutting, represent the essential parts of one of the connectors employedin the all relay links of this system. For purposes of simplicity, various special features of this eonnectar, such as restricted service; reverting cal-l facilities, timing of 'permahents" or shorted lines; and incompleted calls, and the timin of conversations, have been omitted. For similar reasons, the finder end of the link has also been omitted, together with the associated allotter or l'i'n selector, common control relays, and line eireuit. These parts are not considered ne'cessary to an understanding of the invention, and furthermore, are very similar to those disclosed the Patent No. 2333;0'3'9- issued to Edward S.

Peterson, previously mentioned. The same 3'-' relay line circuit is employed} with the same cut-off and lockout relays ink series, andp'r'ovisi'o'rrs for disconnecting the line control or C lead through the finder from the associated control normal or CN lead to the connector termihals, whenever the line relay of the Iinecircuit is operated, and" for reconnecting them when the line relay is restored to normal. The finder is alsoidentical, with the same arrangement of tens and units relays, and the units divided into the same twosub-groups 1 to 5 and 6 to 0, controlled by five unitsrelays and one sub-group relay;

Figs. 6 to 8 inclusive, when likewise arranged as' indicated in Figure 11", with respect to one another and the connector, represent the various types of additional equipment required to provide the automatic trunk selecting features already mentioned. In Fig. 6; for example, the relays on the left oi the sheet arethe Group access re"- Iays, whose function is to pass trunk calls from the connectors to the pro-per trunk roups, in regular order, by way of the Group select relays on the right of the same sheet. The operation of one of the group select relays, in conjunction with an operated one of the group access relays, extends the units conductors and the busy conductor of the connector, through to the proper group of Trunk select relays such as indicated by the rectangles 655 and 056, or such as shown in the upper part of Fig. 9.

Fig. 7 shows a group..of P. B. X trunk select relays whose function it is to pre-select the next idle trunkih the associated P. B. X trunk group, byprep'aring, in advance, a circuit to the connectofurilt relay or relays corresponding to said nexta-idle'trunk. This circuit becomes eiTective immediately whenever these relays are seized by a connector. The P. B. X select relays are reached directly from the connector, no intervening group access or group select relays bein provided. For this reason, the select relays of this group require separate sets of units-controlling contact springs for each connector.

Fig. 8 shows a separate group of Trunk access relays associated with a second group of trunks in the same tens group, in this case, group 30. The function of these relays is to pass trunk calls from the connectors to the associated trunk group by way of a separate set of trunk select relays, such as indicated in the lower part of Fig. 9, no intervening group select relays being employed. The operation of one of the trunk access relays therefore, extends the units conductors and the busy conductor of the connector direct to the trunk select relays involved.

Fig. 9 shows the arrangement of the trunk select relays, two separate groups being indicated, both associated with the tens group 30. The function of these relays is to pre-select the next idle trunk in the associated trunk group. This they do by preparing, in advance, a circuit to the connector units-relay or relays corresponding to said next idle trunk. This circuit then becomes efiective whenever the trunk select relays are seized by the group access and group select relays or by the trunk access relays.

Fig. 10 shows a schematic layout of the Figs. 1 to 9 on a single sheet with circuit details omitted, and only the basic interconnections indicated in order to more clearly portray the relationships between the various figures. Thus the two rectangles I000 and IOI at the left represent two identical connectors such as shown in the Figs. 1 to inclusive, while the two rectangles I020 and I030 immediately adjacent represent the Group access relays of Fig. 6 and the Trunk access relays of Fig. 8 respectively. The rectangle I040 represents the Group select relays of Fig. 6; the rectangles I050 and I060 on the extreme right of the sheet represent the Trunk select relays indicated at 655 and 656 in Fig. 6; and the rectangle I010 represents the group of trunk select relays shown in the upper half of Fig. 9. Rectangle I000 on the other hand represents the Trunk select relays in the lower part of Fig. 9, and rectangle I000 the P. B, X trunk select relays of Figure '7. With respect to the interconnections, the upper three leads at the connectors, marked GS), GS20, G830 are outgoing group select leads, and directly under these is an incoming group select ground lead marked GSG. Below this are two outgoing group access leads designated GA and GAZ, and underneath this is an incoming units lead, which actually represents the five possible numerical units leads plus the units sub-group lead. Still below all of these are three additional leads to the P. B. X trunk select relays, including an outgoing sub-group select lead and a P. B. X trunk select lead designated US and TS respectively, and a second incoming units lead representing again a possible five units leads and a units sub-group lead. Both sets of units leads are multipled together inside of the connector, as shown in Fig. 4.

To continue the description of the equipment shown in the individual circuit drawings in somewhat greater detail, Fig. 1 shows the incoming end of a connector in one of the finder-connector links of this system. Conductors 80 and SI at the upper left of this figure are the talking conductors from the finder, where of course, they may be connected as required to any calling line, and are so connected, almost instantly, upon the initiation of a call. Conductor 82 is a supervisory conductor from the finder, where it is grounded or not grounded on a call depending on the nature of the calling line, and whether or not reverse battery supervision is desired. Conductor 83 is the line control or "0 conductor to the finder where it is switched through to the line circuit of a calling line at the same time that the talking conductors are connected to the calling line. This conductor is grounded in the connector, immediately upon the seizure of this equipment by a call. Conductor 84 is the hold conductor which is also grounded in the connector immediately upon its seizure by a call, and serves to lock up the operated tens and units relays of the finder preparatory to the release of the allotter and the associated common equipment. Conductors 05 and 86 are looking conductors, which are opened in the connector upon its seizure to prepare the release of the associated link select relay in the allotter, thereby to permit pre-selection of the next idle link. The other, open ended conductors in this figure go to the tone and timer equipment, the ringing interrupter and the ringing generator as indicated. The ringing interrupter places negative battery on conductor 88 during each ringing cycle, and momentarily on conductor 89 just before the start of each ringing cycle.

Fig. 1 also comprises ten relays as shown numbered I00 to l00 inclusive. Relay I00 is a switch through relay which operates on a call to a trunk, to by-pass the talking condensers and connect the talking conductors straight through to the trunk repeater, which then takes over the normal function of the connector such as timing, pulse repeating, and the like. Relay H0 is the connector line relay, which operates over the talking conductors 00 and 8| upon seizure of the connector, and cause the operation of the release relay I30 and the hold relay I40. Relay I20 is the battery reversing relay, normally controlled from the back bridge relay I60. Relay I50 is the counting chain release relay which controls the resetting of the pulse counting relays after each digit of the call number dialled by the calling party. Relay H0 is the ringing digit switching relay which operates upon the dialling of the ringing digit to prepare the ringing circuits; relay tail is the pickup relay which operates from the ringing interrupter to assure that the ringing current will be connected to the called line only at the start of a ringing cycle; and relay I00 is the ring-cut-oir relay which operates to stop the ringing, when the called party answers.

Fig. 2, which is a continuation of the connector circuit, consists also of ten relays, numbered 200 to 290 as indicated. Relay 200 i a drain relay,

amen-sec which operates in conjunction with the ring coding relay 220, to prevent ringing voltages from being stored up in the line. Relay 2 I is the ring switching relay, which is controlled from the sixth counting relay, and determines which side of the called line is to be rung. Relays 230 and 24!] are the busy test and idle test relays, which determine the busy or idle condition of the called line, relay 25E) is the preliminary digit switching relay, and relays 281! to 280 are digit transfer relays which operate in succession after the first, second and third digits of a local call number, to prepare various switching and control circuits which will be discussed in more detail in the description of the operation. Relay 2% on the other hand is a dialling transfer relay, which operates on each digit of a call number, to hold the switching circuits open during the actual pulsing, and releases to close them after each digit,

Fig. 3-contains ten counting chain relays designated 311] to 3&0 inclusive and three counting chain control relays am, 320', and 330. These counting relays control the outgoing switching circuits of the connector, and operate in response to the dial pulses, as repeated over the pulsing circuit of the connector. The counting relays operate in succession during the first half of each pulse, and a counting control relay operates in series with them during the second half oi each pulse, each pair of relays being released when the succeeding pair operates. The counting control relays are used reflexively, so that relay am will operate with counting relay '3 Hi, and also with relays 349, 319 and 30B. Likewise, relay 320" will operate with counting relays 320, 350 and 388, and relay 333 with counting relays 330, 3-88 and 390. The last operated relays complete the switching operations required, between digits, and then also release, in preparation for the succeeding digit.

Fig. 4 shows a portion of the connector tens and units relays, together with the units switching or sub-group relay 4%. Only one tens or group relay is shown, that being the relay 470 in the upper right corner of the sheet, representing the first tens group, also designated as group TIO. These tens group relays are operated selectively by the counting relays in response to the dialling, and when operated connect the outgoing talking and control conductors of all ten lines or trunks in that group to the switching springs of the various units relays. To save space, only 4 lines are shown outgoing from relay 410, these being the first, fifth, sixth and tenth, or more properly, lines H, l5, l6 and I0, represented by the four sets of three conductors each, extending to the right from relay 410. In a fully equipped 100 line switchboard, ten of these relays would be required in each connector. A total of five units relays is also provided in each connector, although only two are shown in Fig. 4. These are the relays 4H] and 450 representing the units 1 and 6, and and 0 respectively. The units relays are also operated selectively by the counting relays, or indirectly by the trunk selecting relays, and when operated, each relay erves to connect two sets of talking and control conductors from the tens relays to the break-make springs of the units switching relay. As to which of these sets is actually connected through to the talking and control conductors I58. I65 and 2l5 in the connector, depends on the position of the units switching relay 4B!) which is also controlled from the counting relays or from the trunk selecting relays in the same manner as the units relays, to determine the units sub-group. With relay 400 normal, the .1 to '6 sub-group is involved, and with relay 4'00 operated, the 5 to 0 sub-group is indicated. Thus with relays Mil and 4H] operated, if relay 400 is normal, the connector will be cut through to line H, by way of back contacts 4!", 402 and 404, make contacts 4| l, 4E2 and 413, and make contacts 415, 416 and 411.; while if relay 400 is operated, the connector is cut through instead to line 16, by way of make contacts 4M, 4'02 and 404, make contacts 414, 415 and M6, and make contacts 48-1, 482 and 483. And so on, for the entire ten lines of the group controlled by the group relay 410 In Fig. 5 are shown additional tens or group relays designated 520, 539 and 550 representing groups 20, 3'0 and 50 respectively. Each of these relays is identical with the group relay 470 of Fig. 4, and operates similarly, except that group relay 1550 is associated with the P. B. X trunks. As in the case of relay 413, only four sets of line conductors are shown outgoing from each of these relays, all having corresponding values. Thus with reference to group relay 520, the four lines indicated represent the lines 2!, 25, 2B and 20, in that order, while the four lines shown outgoing from the springs of relay 5% represent the lines 3|, 35, 36 and 30. And for relay 550, the outgoing lines shown are the lines 5|, 55, '56, and 5B. These group relays operate from the counting relays, in conjunction with the units and subgroup relays to select the dialled line, exactly as eX- plained for the group relay 41E of Fig. 4.

In Fig. 6, a group access relay such a 616, 820 or 63!] is provided, for each connector in the system, although only three are indicated in this case. These relays operate when seized by the associated connector on a trunk call and connect the units switching leads from the connector through to the group select relays to the right of this figure. The group access relays are operated only momentarily, and are provided with a special lockout chain which prevents a second rela operating while any other relay is operated, in order to prevent, or reduce the likelihood of, double con nections. Lockout relay E40 and kick-off relay 650 are common relays which are also a part of the group access relays. Relay 646 operates momentarily when any access relay is operated, to open the operate circuit of the other access relays, and if the call is not cut through promptly, relay 65B restores to give the busy signal and at the same time preselect the next idle trunk. A group select relay, such as 660, 618 or 636 in Fig. '6, is provided for each tens group to which toll or interofiice trunk groups have been assigned. These relays operate from the tens relays in the connector, from a special ground provided by the group access relays, and extend the units switching leads from the operated access relay, through to the proper trunk select relays.

In Fig. '7 is shown a complete set of trunk select relays for a P. B. X trunk group having a total of ten trunks. In practice, in a small town, such a large group of P. B. X trunks would seldom if ever be required, and the number of relays would be reduced accordingly. However, the complete set is shown here, to better indicate the arrangement. The relays shown in the lower row, such as H0, 120, etc., are the trunk busy relays, one of which is required for each trunk in the group except the last. This applies regardless of the number of trunks involved. One of these relays is connected to the test conductor of each trunk in the group but the last, and operates from ground on this lead Whenever the associated P, B. X trunk is engaged. The relays shown in the upper row, such as H5, 125, etc., are the trunk select relays, and one of these is required for each P. B. X trunk in the group. They are controlled entirely from the trunk busy relays, and no more than two of these relays including the first, can be operated at any given time. The function of each of these relays is to prepare a circuit to the corresponding units relay or relays in the connector, which circuit is completed in response to the dialling of the third digit in the P. B. X call number. Since no locking circuit is provided, the first idle trunk is selected in all cases. Separate sets of units and sub-group contacts must be provided on these relays for each connector in the system.

In Fig. 8, a trunk access relay such as 8|0, 820, or 830 is required, for each connector in the system, although here also, as for the group access relays, only three are shown. These relays operate momentarily when seized by the associated connector over the separate access leads provided, and serve to connect the units switching conductors from the connector, direct to the special group of trunk select relays in the lower part of Fig. 9. The arrangement of the trunk access relays is identical with that of the group access relays of Fig. 6, except for the omission of the group-select-ground springs such as 6| I. These springs are not required in this case, since no group select relays are used. Relays 840 and 850 are the lockout and kick-01f relays corresponding to the relays 649 and 650 of Fig. 6. The arrangement of these relays is again identical, except that the lockout relay 8&8 provides the trunk select relays with the units operate ground normally obtained from the group select relays of Fig. 6.

In Fig. 9 is shown the basic circuit for the regular trunk select relays, two separate rela groups being shown, each equipped to handle three trunks. In these circuits, a trunk busy relay such as 9H1 or 959, and a trunk select relay such as 915 or 955 is required for each trunk in the group. Each trunk busy relay is normally operated, through a series of break contacts in the associated trunk repeater, and releases whenever the trunk is seized by a call, whether incoming or outgoing. The trunk select relays operate one at a time in rotation, under the control of the trunk busy relays, to preselect the next idle trunk. As each select relay operates, it releases the previously operated select relay, and prepares the circuit of the proper units relay in the connector. Ground for the operation of the connector units relays is received from the group select relays of Fig. 6 or the trunk access relays of Fig. 8 as required. Relays 940 and 980 are reset relays whose function it is to re-set the select chain after the last trunk has been seized, and relays 945 and 985 are all-trunks-busy relays, which control the various counting meters indicated, suchas, if desired, a peg count meter, an all trunks busy meter, and an overflow meter.

Both sets of trunk select relays in Fig. 9 are identical and are, as stated, associated with the same tens group. Their select springs are also associated with the same units relays, namely 1-6, represented by connector relay M0, and 2-7 and 3-8, not shown. In the lower set of trunk select relays in Fig. 9, however, the upper select springs are wired to the units switching or sub-group conductor, such as 996. By this means, the upper set of relays is made to serve the #1, 2 and 3 terminals of the 30 group tens relay in the connector to which the first three trunks are assigned, while the lower set is made to serve the #6, '7 and-8 terminals of the same tens relay to which the second three trunks are assigned.

These trunk groups of course, can be readily expanded, contracted or rc-arranged in almost any manner desired within the tens group, assuming that corresponding changes are made in the trunk select relays, and any line terminals not used for trunks may be assigned to subscribers lines. The same thing applies to the more usual case where but one trunk group is assigned to any one tens relay, as with the select relay sets indicated by the rectangles 655 and 656 in Fig. 6. Such groups may include as many as ten trunks if desired. This of course would require a full set of ten select relays, with the units switching lead connected up in five of them, and not connected in the other five.

Numbering scheme The switchboard is normall arranged so that toll trunks and inter-ofiice trunks are assigned to tens groups It), 20, 30 and 40, while P. B. X trunks are assigned to tens groups 50 and 60. The trunk groups usually start on the first terminal and use successive terminals of the tens group, in order to facilitate expansion. This is not essential however. Subscriber lines may be assigned to any tens group where terminals are available.

T011 and inter-ofiice trunks are seized, in all cases, by diallin a single-digit number. These single-digit numbers are 0, 9, 8 and 7. Normally, the digit 0 operates group relay #10 (tens relay 410), the digit 9, group relay #20 (tens rela 520), the digit 8, group relay #30 (tens relay 530), and the digit '7, group relay #40, not shown. In the arrangement employed in the present disclosure however, both of the digits 8 and 7 will operate group relay #30, thus eliminating the need for group relay #40, or freeing it for other uses, such as calls to subscribers lines entirely. On all trunk calls, the proper units relay is operated automatically, from the trunk selecting equipment, as previously indicated.

Subscriber call numbers consist invariably of four digits, always beginning with a preliminary digit 2, followed by a variable tens digit, a variable units digit, and a variable ringing or code selecting digit. The last three digits may be any digit from 1 to 0 inclusive, or as permitted by the assignment of trunks.

P, B. X call numbers also consist of four digits, the first or preliminary digit being always 2, the second or tens digit either a 5 or a 6, the third or units digit a l, and the fourth or ringing digit also a 1. The complete call numbers would thus be either 2511 or 2611. The units digit 1 in this case, may or may not operate the first units relay, as this depends entirely on the idle or busy condition of the first P. B. X trunk. The final digit "1 selects the first ringing code in all cases. This consists of a single long ring of about two seconds duration, repeated intermittently.

To summarize briefly:

1. A first digit 0 indicates a call to a toll trunk;

2. A first digit 9, 8 or 7 indicates a call to an inter-office trunk;

3. A first digit 2 indicates a call to a subscribers line or to a P. B. X trunk;

l. Frst digits 1, 3, 4, 5 or 6 are not used, and if dialled,.inadvertently or otherwise, they are absorbed, and are thus for all practical purposes without effect.

The general description of the. apparatus and its general method of functioning having been completed, a, detailed description of the operation of the circuits, will now be. given, by actually following; a. typical; calls. through the system,

Seizure of the connector When a finder, upon the initiation of a call, connects the calling line through to the associated connector, the connector line relay IIII operates over the. calling; line loop as follows: ground through the upper winding of relay H; break. contacts I21, break contacts IUI, line conductor 80, through the calling subscribers line and telephone instrument, back over line conductor 8|, through break contacts I02, break contacts I22, and the lower winding of relay H'EI to negative battery,

The connector line relay III] operating, at make, contacts I I I closes a circuit from ground through break springs I96 to release relay I which operates. The release relay I30 in turn, at make contacts I'3I closes an obvious circuit: to the hold relay I40, which also operates The hold relay I upon operating, at make contacts I44 connects ground from make springs I3I to the control conductor 83 and thence back through the finder of the link to the cut-off and lockout relays in the line circuit of the calling line, which relays operate in series and disconnect the line relay of the line circuit from the line. The subscribers line relay thereupon restores to start the release of the allotter and at the same time re-connects the control and control normal leads together as previously mentioned.

The hold relay I40 also, at make contacts I49 connects ground to the tone and timer start conductor 81 in order to start the timing and tone generating equipment, and at make contacts I 4| connects dial tone to the calling line. This latter circuit extends from ground battery and the secondary of the dial' tone induction coil to the dial tone conductor 249 shown in the upper part of Fig. 2, through, break contacts 2' and 26L conductor I53, make contacts I4I,. conductor I35, line condenser IE9, break contacts I22 and I02, negative line conductor 8|, through the calling subscribers telephone and back over the positive line conductor 80;, and through back contacts IDI and I2I and the upper winding of connector line relay IIII' to ground. Dial tone is made audible at the calling telephone over this circuit as an indication that dialling may proceed.

The hold relay also, at make contacts I42 prepares locking circuits for relays I20, no, 210, 23d, and the counting relays of Fig; 3'; at make contacts I43 prepares the pulsing circuit; at make contacts I45 prepares a circuit for the test relay 245i; and at make contacts I 4E prepares locking circuits for test relay 240, and for the transfer relays 260, 210 and 280. Finally at make contacts I41, relay I411 grounds the hold conductor 34 back to the finder to hold the finder tens and units relays operated, and at; break contacts its opens a locking circuit to the associated link select relay in the allotter, by way of the locking conductors 85 and 86, thereby to permit the release of this relay and the preselection of the next idle link,

Call to d subscribers station- The connector is now ready for dialling, with the line, release, and hold relays IFEI; I30 and I40 operated, The operation on av call to a regular subscribers station. will be described. first, it being understood that a 4 digit number starting with the digit 2- is. used on all such calls. Sub.- scribers lines may appear of course in any tens group, but for. purposes of illustration it will be assumed: that, the call is to; a station having the call number 2151'. The; calling subscriber on hearing the dial tone, proceeds therefore to dial the first digit 2.

The. connector line:- relay III]- follows: the dial pulses and' at each pulse, its make contacts III momentarily open; the circuit of release relay I38. Becauseoi the: slow release nature of relay I39 however, due to the use of av copper sleevev over the coil, this relay is} not outwardly affected and remains operated. At each release of the line relay also, its break contacts Ht momentarily close the pulsing circuit to the counting relays, and to the transfer relay 29.0 which is. in parallel with. this circuit. Relay 293: operates on: the first pulse, and because of its slow release nature, due again. to. the use of: a. copper sleeve over the coil, remains operated; during: the succeeding pulses of each. digit, releasing shortly after the end of each series of. pulses.

On the first release. at line: relay I. I0: therefore, the back contacts. Ilil close a circuit to. the pulsing relay 31.0 as follows:- ground at: break contacts H35, break contacts lilli, make contacts I43, break contacts I'IIL, conductor I19; break contacts 234, conductor 2% left, break contacts 333, break contacts. 323, break contacts 313:, and the winding of the counting relay 3N4]: to negative battery. A branch of this circuit alsoextends from break contacts 234' over conductor 2663 right, to the winding of transfer relay 290 and negative battery.

Relays 290 and 310 operate over this circuit, the principal function of relay 291] being at this time to-open the grounding circuitsto the springs of the counting relays. The counting relay 346, at its make contacts 3', extends its operating ground to the winding of the counting control relay 3H5". This latter relay is: not affected at the moment however, due to having ground also on the other side of its winding, from make contacts I42, by way of break contacts I5I and H33, conductor I615, break contacts 233, conductor 295, and break contacts 324'. Relay 311) also, at make contacts 316, prepares the operate circuit. of the next counting. relay 32B.

Upon the re-energization of line relay- I IIl, at the end of the first impulse, make contacts I'II re-close the circuit of release relay I38, while break contacts I;I I open the pulsing circuit momentarily to the transfer relay 290 and counting relay 3w. Relay 29h maintains its armature in the operated position during this interval, due to its slow to release nature, as previously mentioned. The opening of: the operate circuit to the pulsing relay 3I0 however, removes the short circuit from the winding of the counting control relay 316". Relay Milt" thereupon: operates in series with relay 3W locking the latter relay in its operated position over the following circuit: ground through make contacts L42, break contacts I5I break contacts I 03, conductor I53, break contacts 233, conductor 2D5left, break contacts 3Z4, winding of relay 3113-, make contacts 3H, and the winding of relay 319 to negative battery.

Relay 3 I 6 upon operating, at its break contacts- BIB disconnects the pulsing circuit from the operating circuit of counting relay'3I-Il and at make 1 1 contacts 3I3' connects it to the operating circuit of counting relay 320 by way of make contacts 3I6. The operation of the remaining contacts on relays 3H! and 3I9 is without efiect at this time.

Upon the next release of line relay H0, at the start of the second impulse of the first digit 2, make contacts III again open the circuit of release relay I39 momentarily, while the make contacts III again connect ground to the impulsing.

circuit momentarily. Counting relay 320 operates over this circuit which as before is from ground at break contacts I 96, through break contacts III, make contacts I43, break contacts I1I, conductor I19, break contacts 234, conductor 206 right to the winding of relay 299, conductor 206 left, break contacts 333 and 323 and thence through make contacts 3I3 and 3I9, and the winding of relay 320 to negative battery.

Counting relay 320 upon operating, at make contacts 323 prepares a circuit to the preliminary digit switching relay 259, at make contacts 329 prepares the operating circuit of counting relay 339, and at make contacts 32I extends its own operating ground to the winding of the counting control relay 320'. Relay 320' does nothing however, at the moment, because of also having ground on the other side of its winding, from make contacts I42, by way of conductor 28%). Relay 290 remains operated.

Upon the next re-energization of line relay lit], at the end of the second and final impulse of the first digit, make contacts III again close and re-establish the circuit of release relay I39, while break contacts III open and again remove pulsing ground from the pulsing circuit, thereby opening the operate circuits to relays 299 and 329. This removes the short circuit from the counting control relay 320 and this relay therefore operates in series with counting relay 320 over the following circuit: ground through make contacts l42, break contacts I5I and I93. conductor I91, break contacts 233, conductor 295, break contacts 334, winding of relay 320', make contacts 32I and the winding of relay 320 to negative battery.

Relay 329' upon operating, at break contacts 324 opens the locking circuit of relays 3H) and 3| 0, whereupon both of these relays release. Relay 320 also, at break contacts 323' disconnects the pulsing conductor 206 from the operate circuit of counting relay 320, and at make contacts 323 connects it to the operate circuit of counting relay 339, by way of make contacts 326. Finally, relay 320 at make contacts 325', grounds conductor 204 leading to break springs 294 on the transfer relay 299. The other contacts of relay 320 are without effect at this time.

Transfer relay 290 now releases, after a short delay, and at break contacts 294, 293 and 292 connects ground to conductors 253, 254 and 259 and thence through the cable 221 to the springs of the counting relays. This circuit is from ground at make contacts I42, conductor I66, conductor 203, make contacts 325', conductor 294, conductor I99 right, and break contacts 294, at which point the circuit divides and goes on to the counting relays over three separate paths. One of these paths is through break contacts 292, 264 and 215 and the conductor 253 to the counting relays, where only open contacts are encountered. This branch is therefore without effect at this time. A second path is through break contacts 265, 216, 211- and 293, and the conductor 259 to the count-- ing relays, where again only open contacts are encountered. This branch is therefore likewise without eiTect when a 2 is dialled. The third path is through break contacts 265, break contacts 216, conductor 254, through cable 221, conductor 254 in the counting relays, make contacts 323, conductor 226, and the winding of relay 250 to negative battery.

The preliminary digit switching relay 250 now operates, and at make contacts 25I extends its operating ground to the winding of the preliminary digit transfer relay 219. This latter relay however, has ground also on the other side of its winding, from conductor I84 left and make contacts I43 on the hold relay, and does nothing at the moment. Relay 250 also, at make contacts 252 completes a circuit to the counting chain release relay I59 as follows: ground from make contacts I46, through conductor I84, make contacts 252, break contacts 214 and 253, conductor I86,

and the winding of relay I553 to negative battery.

The counting chain release relay I59 operates momentarily over this circuit, and at break contacts I5I disconnects ground from the conductors I91 and 295, and hence from the counting and counting control relays 32!] and 329, which as previously explained, are held locked in series over these conductors from the ground at make springs I 42. Relays 329 and 322' thereupon release and restore their springs to normal. The opening of make contacts 325 and 323 opens the operate circuit of the preliminary digit switching relay 250. This removes the ground shunt from the preliminary digit transfer relay 219, permitting the latter relay to operate in series with relay 259 and locking both relays operated. The locking circuit for these relays is from the ground at make contacts I49, over conductor I84, through the windin of relay 212, make contacts 25!, and the winding of relay 250 to negative battery.

The preliminary digit transfer relay 213 upon operating, at break contacts 211 obviously opens the dial tone circuit to the calling line, and at make contacts 212 prepares an alternative circuit for the transfer relay 296 from the pulsing circuit, shunting the break contacts 234 on the busy relay 239. At break contacts 213 relay 219 opens the circuit of the switch-through relay I 93, and at make contacts 213 prepares a circuit for operating the counting chain release relay :52 from the units relays. Relay 210 also, at break contacts 214, opens the original circuit to relay I59, therc by causing the release of this relay, and at make contacts 214 prepares a circuit for operating relay I59 from the tens group relays. Finally, relay 210 at contacts 215, 216 and 211 opens the circuits leading to the counting relay conductors 253, 254 and 259, and prepares circuits to the conductors 255 and 256 leading to the group selecting springs of the counting relays. Connector relays I I0, I39, I49, 259 and 219 are now operated.

The second digit of the call number 2151 causes line relay I ID to release and re-operate once only, in response to the second operation of the dial. On the break of the pulse, when relay H9 releases, transfer relay 299 and counting relay 3I0 again operate in parallel over the pulsing conductors I19 and 2.95, from the ground at break springs I65, as previously explained. Release relay i39 remains operated as usual, since its circuit is only broken momentarily at make contacts III. On the make of the pulse, When line relay IIO re-operates, the circuit of release relay I39 is reestablished and the operate circuit of relays 299 and 3I9 is broken. The opening of the 0perate circuit of the counting relay 3IEI permits the operation of counting control relay 3I0' as before, in series with countin relay 3I0, from ground at make springs I42, by way of conductors 561 and 205, and break springs 324. Relay 3!!! therefore remains operated.

Transfer relay 290 releases however, after a short delay, and at break contacts 294 and 292 connects ground to conductors 255 and 256 and the associated group springs of the counting relays. This circuit is from ground at make contacts I42, over conductors I65 and 23, through make contacts 3I5', conductor 204, conductor I98 right, and break contacts 294, at which point the circuit divides and goes on to the springs of the counting relays over two separate paths. One of these paths is through break contacts 265, make contacts 2'i6, and conductor 255 to the counting relays, where only open contacts are encountered. The other circuit is through break contacts 292, break contacts 264, make contacts 215, conductor 255, over the cable 221, conductor 255 at the counting relays, make contacts 3I4, conductor 42 I, and the winding of the first tens-group relay 410 to negative battery.

Tens relay 410 operates over this latter circuit and closes its contacts, thereby preparing circuits to all of the lines in the called line tens group. At make contacts 414, group relay 410 extends its own operating ground to the winding of the tens digit transfer relay 260, by way of conductor 2I1. Relay 269 does nothing at this time however, due to having ground also on the other side of its winding from make contacts I46, through conductor I04. Group relay 410 also, at make contacts 413 completes a circuit for the operation of the counting chain release relay I50 as follows: ground at make contact I 56, conductor I84, make contacts 413, conductor 225 down, make contacts 214, break contacts 293, conductor I86 and the winding of relay I50 to negative battery.

The counting chain release relay I50 operates over this circuit and at break contacts I5I disconnects ground from conductors W1 and 205 and hence from the counting and counting control relays 3i and 3 I 0 which are held locked in series over these conductors from ground at make contacts I42. Relays 3 I0 and M0 thereupon release and restore their contacts to normal. The opening of make contacts M and 354 opens the operate circuit to the group relay 410. This re moves the shunt from the winding of the tens digit transfer relay 260, whereupon relay 260 operates in series with relay 410 and locks the latter relay in its operated position over the following circuit: ground at make contacts I 46, conductor I84, winding of relay 260, conductor 2I1, make sp ings 14, nd he Winding of relay 410 to negative battery.

The tens digit transfer relay 260 upon operating at break contacts 26E opens a second point in the dial tone circuit. and at make contacts 262 prepares a circuit for the units switching or sub group relay 400, over conductors 2I3 and 2M. Relay 260 also, at break contacts 263 opens the circuit to the counting chain release relay I50 causing this relay to release, and at make contacts 266 grounds the ringing machine start lead I98 by way of conductor l9? and break contacts I15. Finally, relay 260 at break-make contacts 264 and 265 opens the circuits leading to the counting relay conductors 255 and 256 associated with the tens selecting springs, and prepares circuits to the conductors 251 and 258 leading to the units selecting springs of the counting relays.

and make contacts 336.

14 Connector relays IIO, I30, I40, 250, 260, 210 and 410 are now operated.

The third digit of the call number 2151 causes the connector line relay IIO to release and reoperate five times, the transfer relay 290 operating as before on the first pulse, in parallel with the pulsing circuit, and remaining operated until shortly after the last pulse of the digit, since it is re-energized momentarily at each release of relay H0.

At the first release of relay IIO therefore, relay 290 and the counting relay 3I0 operate from break contacts III, over the pulsing conductors I 19 and 206, relay 3I0 preparing its own locking circuit as before at make contacts 3! I, and at make contacts 3 I 6 preparing the circuit of counting relay 320. On the re-operation of relay II 0, the pulsing circuit is opened as before at break springs III, and counting control relay 3I0' operates in series with the first counting relay 3I0, from ground on the locking conductors I61 and 205, by way of break springs 324 and make springs 3| I. j

At the second release of relay IIO, counting relay 320 operates from ground on the pulsing conductors I19 and 206, by way of make contacts 3I3 and 3I6. Relay 320 at make contacts 32I prepares its own locking circuit, and at make contacts 326 prepares the circuit of counting relay 330. On the re-operation of relay I I0, break contacts III again remove ground from the pulsing conductors I19 and 206 whereupon the counting control relay 320' operates in series with the second counting relay 320, from ground on the locking conductors I61 and 205, by way of break springs 334' and make springs 32I. Relay 320 at break-make contacts 323' disconnects the pulsing conductor 206 from the counting relays 3I0 and 320 and connects it to the counting relay 330.

. Relay 320' also at break contacts 324 open the locking circuit of relays 3I0' and 3| 0, causing the release of these relays.

At the third release of relay IIO, counting relay 330 operates over the pulsing conductors I19 and 206, by way of make contacts 323 and 326. Relay 330 at make contacts 33I prepares a, locking circuit for itself and at make contacts 336 prepares the operate circuit of counting relay 340. On the re-operation of relay IIO, break contacts iII again open the pulsing circuit to conductors I 19 and 206, and on the removal of its ground shunt, counting control relay 330 operates in series with counting relay 330 from ground on the locking conductors I61 and 205, by way of break springs 3I4' and make springs 33I. Relay 330 at break make contacts 333' disconnects the pulsing conductor 206 from the counting relays 3I0, 320, and 330 and connects it to the fourth counting relay 340, Relay 330 also at break contacts 334' opens the locking circuit of relays 320' and 320, and causes the release of these relays.

At the fourth release of relay II, the fourth counting relay 340 operates from the pulsing conductors I19 and 206, by way of make contacts 333' Relay 340 at make contacts 34I preparesa locking circuit for itself through the winding of counting control relay 3I0', and at make contacts 346 prepares the operate circuit of counting relay 350. On the reoperation of the relay II 0 ground is again removed from the pulsing conductors I19 and 206 and hence from the operate circuit of counting relay 340, whereupon the counting control relay 3I0' operates in series with relay 340, from ground on the locking conductors I61 and 205,

by way of "break springs 324 and make :springs 34L Relay m upon operating, at make contacts 3 I3 further prepares the operate circuit for counting relay 355, and at break contacts 314 opens the locking circuit of relays 330 Land 1330, whereupon these relays release.

.At the fifth :release of relay I H the fifthcounting relay E58 operates from pulsing conductors IiSa-nd byway of break contacts 333 :and 323', and make contacts 3l3 and 345. Counting relay 35.5 at make contacts prepares a looking circuit for itself through the winding of relay 328" and at make "contacts 356 prepares the 0perate circuit of counting relay 35.3. On the reoperation of relay H 9, removal of pulsing ground from the pulsing conductors H9 and 2:36 and hence from the operate circuit of the counting relay 355 permits the operation of counting control relay 322' in series with relay 350, from ground "on the locking conductors I67 and 255, by way of break springs 32 i and make springs 535i... Relay 32S upon operating, at make contacts 323' further prepares the operate circuit of counting relay see, and at break contacts '324' opens the lock ng circuit of relays 3M and 34!], causing the release of these relays. The other contacts of relay 323' have no particular functions :at this time, although make contacts 32! close an alternative circuit to the ringing machine start conductor 193 from ground through make contacts 2265 and conductor 201. The original :circuit, through make contacts 26-5, conductor 18"? and break contacts H5 remains intact however, for the time being.

Transfer relay 29s now releases, shortly after the fifth and last digit, and at break contacts 294 and 2.92 connects ground to conductors 25'! and 258 and thus to the associated uni-ts springs of the counting relays. This circuit starts as before from ground at make contacts M2, and passes through conductors F85 and 2113, make contacts 325, conductor 2%, conductor I99 right, and break contacts 2%, at which point-the circuit divides and proceeds over two separate paths. One of these paths is through make contacts 265, break contacts 285, conductor 258, cable 221, and conductor 2558 again in the counting relays, where only open contacts are encountered. The second path is through break contacts 292, make contacts 256. break contacts 285, conductor 251, cable 221, conductor 25? in the counting relays, make contacts conductor 435, and the winding of the 54) units relay 455 to negative battery.

The units relav 55! o erates over this circuit, and at make contacts and 452 extends the talking conductors of the connector to the called line I15. Thus, the talking conductor i5'8 in the upper part of Fig. 4, is connected through break contacts 45!, make contacts 45'! and make contacts 418 to the line conductor l5, while talking conductor I is connected through break contacts .62, make contacts 452 and make contacts M9 to the line conductor l 5'. S milarly, test conductor H5 is connected through break contacts we and. make contacts 453 and 480 to the test conductor 55'' of the called line. which will be assumed to have negative battery on it, indicative of an'idle line.

The units relay 55 also, at make contacts 5-58, extends its own'operat ng ground to the winding of the units digit transfer relay 288, by way of conductor 2l8. Relay 288 is not afiected at the mom nt however. due to hav ng ground also on the other side of its windin from conductor I84 and make contacts [516. Finally, relay 459 at make contacts 457, completes 'a circuit to the counting chain release relay I55 as follows:

ground at make contacts M6, conductor l84,

make contacts E57, conductor 2L9, make con- 5 tacts 2'13, break contacts 284, conductor I85, and

the winding of relay I55 to negative battery.

The counting chain release relay i551 operates over this circuit, and at break contacts [5| disconnects ground from conductors l5! and 255, to which the counting and counting control relays 359 and 326 are held locked in series, as previously explained. Relays 358 and 32B therefore release and restore their contacts to their normal position. When the make contacts 325' and 355 open, they open the operate circuit to the units relay s56. This removes the ground shunt from the winding of the units digit transfer relay 283. Relay 23o thereupon operates in series with the units relay 452i, and locks the latter relay operated, from ground at make contacts I46, by way of conductor I8 3, the winding of relay 285, conductor 2i8, make contacts 458, and the winding of relay 456 to negative battery.

The units digit transfer relay 280 upon operating, at break contacts 285 opens the circuit to the counting chain release relay l 55, causing the release of this relay. At break contacts 285 and 236, relay 28%) opens the circuits to conductors 25 i and 258 leading to the units springs of the counting relays, and at make contacts 285 prepares a circuit to the ringing digit switching relay ill At break-make contacts 28L relay 285 disconnec s the units switching or subgroup relay 458 from conductor 2l3 leading to springs on the sixth ounting relay, and connects the ring switching or side-of-line-sele'ct relay 2H! to the same conductor 2l3. At make contacts 282 relay 28E! prepares an alternative looking circuit for the counting relays, shunting break contacts 233 on the busy relay. This action is without significance at this time, however. Final y, at break-make contacts 283, relay 28B disconnects the busy test relay 230 from the test conduc or 2!?) and connects the idle test or switching relay 24H thereto in its stead.

The called line being idle, as stated. a circu t for the operation of the idle test relay 245 is now established as follows: ground at break contacts lli'i, through make contacts M5, conductor $83, upper winding of test relay 250. break contacts 235, make contacts 283, test co ductor 215, break contacts 404, make contacts 453, make contacts 688, line test conductor 15" and the windings of the cut-01f and lockout relays in the line circuit of the called line to negative battery. The line cut-off and lockout relays operate over th s circuit to clear the called line of attachments in the usual manner.

The idle test relay 24!] also operates and at its preliminary make contacts 244 looks itself through its lower winding to the locking ground on conductor I84, from make contacts I46. At make contacts 24! and 242, relay 24B prepares circu ts for connecting ringing signals to the called line. At make contacts 243. relay 240 connects direct ground from conductor I83 to the l ne test conductor, by way of break contacts 235,

make contacts 283 and the connector test conductor 2E5. At make contacts 245. relay 24o also prepares a circuit to the ring pickup relay E80. Finally, at make contacts 246, relay 2G8 prepares a start circuit to the ringing interrupter. Connector relays H8, I30, I40, 240, 255, 26!], 27B, 280, 450 and 410 are now operated.

The fourth and last digit of the call number 2151 now causes the connector line relay IIO to release and re-operate once only. Upon the release of relay IIO, the closure of the break contacts III sends a pulse of current over conductors I19 and 206 as before, to again cause the operation of transfer relay 299 and counting relay 3I0. Upon the reoperation of relay IEO, the opening of the break contacts I I I opens this circuit and permits the counting control relay 3I0' to operate in series with the counting relay 3I0 as previously explained, from ground on conductor 205.

Counting control relay 3I0 upon operating, at make contacts 3! I completes the previously mentioned alternative start circuit to the ringing machine, from ground at make contacts 206, through conductor 201, make contacts 3| I, and conductor I98 to the ringing generator. This circuit shunts the break contacts I15 on the ringing digit switching relay I10, thus assuring continued operation of the ringing machine when relay I operates. At make contacts 3 I72, relay SI?! further prepares the start circuit for the ringing interrupter. Relay 3I0 also, at break-make contacts 3I3 prepares the usual operate circuit to the second counting relay, and at make contacts 3I5 prepares the operate circuit of relay I10.

Transfer relay 290 now restores, after a slight interval, and at break contacts 294 and 292 completes the operating circuit to the ringing digit relay I19, which is as follows: ground from make contacts I42, conductors I99 and 203, make contacts 3I5, conductor 294, conductor I99 right, break contacts 294 and 292, make contacts 264 and 285, conductor I81, break contacts of the make-before-break spring I12, and the winding of relay I10 to negative battery.

The ringing digit switching relay I10 now operates, and at make contacts I12 locks itself to the grounded conductors I89 and 203. At break contacts I1I, relay I10 opens the pulsing circuit to the counting relays, and at make contacts I13 connects the code conductors I94 and I95 together, preparatory to their connection to the coding relay 220. At make contacts I14, relay I10 completes the start circuit to the ringing interrupter as follows: ground at make springs 3I2, conductor 209, make contacts 246, conductor I96,

make contacts I19, and start conductor 90 to the ringing interrupter. Relay I10 also, at break contacts I15 opens one of the start circuits to the ringing machine, and at make contacts I19 connects ground from conductor I99 to one side of the ring pickup relay I80.

When therefore, the interrupter places negative battery momentarily on the pickup lead, just before the start of the next ringing cycle, a circuit is completed for the operation of the ring pickup relay I09 as follows: ground at make contacts I92, conductors I66 and 203, make contacts 3I5, conductor 204, conductor I99 left, make contacts I16, break contacts I62, upper winding of pickup relay I80, conductor I99, make contacts 245, conductor I92, and the break contacts of the make-before-break springs I8! to negative battery on the pickup conductor 89. Relay I80 thereupon operates, and at make-before-break contacts I8I locks itself to steady negative battery from the interrupter on the hold battery conductor 88, and at the same time disconnects itself from the pickup conductor 89. Relay I80 also, at make contacts I32, connects conductor I93 and the coding relay 220 to the code conductors I94 and I95, and thence tothe code springs of the counting relays. Since the interrupter removes negative battery from conductor 88 at the end 18 of the code cycle, this action is repeated at each ringing cycle with the pickup relay I pulling up at the start of the cycle and restoring-at the end of the cycle.

Ground pulses representative of the first ringing code now pass from the ringing interrupter, shown as the rectangle 92 at the lower right in 3, to the coding relay 220 through make springs 3I2 on the operated counting relay 3I0. This circuit is from ground at the coding springs of the interrupter, cable 93 and conductor 3I9, make contacts 3I2, conductor I94, make contacts I82, conductor I93 and the winding of relay 220 to negative battery. For the first code, each code cycle consists merely of one long ring of about two seconds duration followed by a silent period of about three seconds, repeated intermittently until the called party answers. This is the code employed for ringing on single party lines. The interrupter of course, also connects various combinations of long and short coding pulses to the other ringing conductors at the same time, through the cables 93 and 94, but as these circuits are all open at the springs of the other counting relays, this action is without effect in the present instance.

The coding relay 220 follows the code pulses, and on each energization connects ringing current to the called line over the following circuit: the negative out terminal of the ringing machine or ringing generator, the ringing conductor 9| in the upper right of Fig. l, winding of the slow-to-operate ring-cut-off relay I which is shown with a copper sleeve over the core and a copper slug at the armature end, conductor I63, break contacts 2I2, make contacts 223, make contacts 242, talking conductor I65, break contacts 402, make contacts 452, make contacts 419, the called line negative line conductor I 5', through the ringer at the called station and back over the called line positive line conductor I5, make contacts 418, make contacts 45I, break contacts 40I, talking conductor I58, make contacts 24I, make contacts 222, and break contacts 2II to ground. The bell at the called station now rings intermittently, in the usual manner. In the case of a call to a party line, with divided ringing, this circuit of course would go directly to ground at the subscribers ringer instead of returning over the positive line conductor. In this case also, the last digit of the call number, and consequently the ringing code, would be varied as necessary.

Relay 220 also, at each energization, at make contacts 22I completes a circuit for providing ring-back tone to the calling line. A portion of the ringing current passes back over this circuit which may be traced as follows: ringing generator, conductor 9|, winding of ring-cut-ofi relay I90, conductor I 63, the low capacity condenser 2I0, makecontacts 22I, conductor I51, conductor I3-5, talking condenser I09, break contacts I22, break contacts I02, negative line conductor 8|, through the calling telephone, back over the positive line conductor 80, break contacts I01, break contacts I2I, and the upper windin of relay IIO to ground. The ringing current is thereby made audible to the calling subscriber as a low tone,

to indicate that the called line is being signalled.

The ringing current itself is of course prevented from getting into the calling line by the open break contacts 222 and 223 on the one hand, and by the open make contacts I 0| and I 02 on the other hand.

Relay 220 also, at make contacts 224 completes an obvious circuit for operating the drain relay 1 9 I 200. Relay 2'00 therefore follows the pulsations of the coding relay 220, but due to being made slow to release by a copper slug over the core at the heel end, relay 200 remains operated for a short instant, after each release of relay 220. During this interval, at the beginning of each silent period, ground and negative battery from make contacts 20I and 202 are connected momentarily across the called line, by way of break contacts 222 and 223, make contacts 24I and 242, and the talking conductors I53 and I65. This drains the condenser charge from the line caused by the ringing, and prevents the building up of heavy voltages therein such as might otherwise occur, particularly on heavy loaded party lines.

It also tends to prevent premature ring cutoff, caused by premature operation of the ring cutoff relay from the same line charge.

When the called party answers, if the receiver at the called station is lifted during a ringing perioda direct current circuit is completed thereby for the operation of the ring-cut-off relay I90, over the previously traced ringing circuit, that is from negative battery at the ringing generator, to conductor 9i and relay I90, through the called line loop and the called subscribers telephone, and back to ground at break contacts 2I I. The ring-cut-off relay I90 operates over this circuit and at make contacts I 9| completes a circuit to the counting chain release relay -I 50. This circuit is from ground at make contacts I42, conductors I56 and 203, make contacts 315, conductor 204, conductor I99 left, make contacts I9I, and the winding of relay I50 to negative battery,

The counting chain release relay I50 now operates, and at break contacts I51 opens the locking circuit to the counting relays, whereupon the relays 3'I0 and 3I0 both release and restore their contacts to normal. Relay 3I0 upon releasing, at make contacts 3I-I' removes ground from the ringing machine start circuit, and at make contacts 3I2' opens the start circuit to the ringing interrupter, thereby causing both of these devices to stop, provided they are not held operated from some other source, such as another connector, or a repeater. Relay 3I-0 also, at make contacts 2H5 removes ground from conductors 204 and I99. Removal of ground from conductor I99 right, opens the operate circuit to the ringing digit relay I10, but this is without effect, as relay I is now locked to ground on conductors I88, 203 and I66 as previously explained. Removal of ground from conductor "I09 left however, opens the circuits to both of the counting chain release relay I50 and the pickup relay I80, and both of these relays restore. Relay I80, at make contacts I82 opens the circuit to the coding relay 220, which also restores. Counting relay 310 upon releasing, at make contacts 3I2 further opens the circuit of the coding relay 220 by disconnecting the coding conductor 3I9 from conductor 194.

The coding relay 220 upon releasing, at make contacts 22I opens the ring-back circuit, and at make contacts 222 and 223 opens the ringing circuit causing relay I90 to restore. Relay 220, at make contacts 222 and 223 prepares the talking circuit, and at break contacts 224 opens the a circuit to the drain relay 200. Relay 200 now also releases, after a short delay, and .at break-make contacts I and .202 opens the line drain circuit, and connects the called line loop to the backbridge or batter feed relay I60.

The back-bridge relay I60 now operates over the called line loop by way of the following circuit: ground through the upper winding of relay I60, conductor I59, break contacts 20I and. 222, make contacts 24I, conductor "I58, break contacts 40I, make contacts 45I and 418, line conductor I5, through the called telephone to line conductor I5, make contacts 419 and 452, break contacts 402, conductor I65, make contacts 242, break contacts 223 and 202, conductor I64, and the lower winding of relay I60 to negative battery. Relay I60 upon operating, at make contacts IOI completes a circuit for the operation of the battery reversing relay I20 from conductor 82 which is now grounded in the finder. Break-make contacts I62 are also reversed by the operation of relay I60, but without effect at this time.

The battery reversing relay I20 now operates, and locks by way of its make contacts I23 to ground at make contacts I42. Relay I20 also, at its make-before-break contacts I2I nd I22, reverses ground and negative battery from relay I10 to the callin line, for metering or supervisory purposes, as required. The talking circuit through the connector is now complete, and extends from the calling telephone by way of the line conductor 80, through break contacts IOI, make contacts I2I, talking condenser I09, conductor I64, break contacts 202 and 223, make contacts 242, conductor I65, break contacts 402, make contacts 452 and 419, line conductor I5, the called telephone, line conductor I5, make contacts 418 and 451, break contacts 40I, conductor I58, make, contacts 24I break contacts 222 and 20I, conductor I50, talking condenser I08, make contacts I22, break contacts I02, and line conductor 8| back to the calling telephone. Relay I I0 furnishes talking battery to the calling line, and relay I60 to the called line. Connector relays IIO, I20, I30, I40, I60, I10, 240, 250,260, 210, 280, 450 and 410 are now operated.

If, instead of answering during a ringing period, the called party answers during a silent period, the action of the connector is slightly diiferent. In this case, both the coding relay 220 and the drain relay 200 will be at normal, so that when the called party answers, the back bridge relay I60 finds itself connected to the called line loop, instead of the ring-cut-off relay I00. Relay I63 therefore operates immediately, while relay I90 remains normal. Relay I60 at make contacts I'6I, pulls the battery reversing relay I20 as before, and at break contacts I 62 opens the circuit of pickup relay I which restores and prevents any further operation of relay 220. Relay IEO also, at make contacts I62 completes a circuit to the counting chain release relay I50 from ground on conductor I99 through make contacts I16 and 3I5'. The counting chain release relay I50 operates over this circuit and at break contacts I'-5I opens the locking circuit to the counting relays, whereupon the relays 3I0 and 3I0 restore. Relay 3I0' as before at make contacts 3I I opens the ringing machine start circuit and at make con-tacts 3-I2' opens the interrupter start circuit. Relay 3I0 also, at make contacts 3I5', removes ground from conductors 204 and I99, thereby causing the counting chain release relay I50 to restore, Counting relay 3I0 upon releasing at make contacts 3I2 disconnects the coding conductor 3I9 from conductor I94. The connector is now ready for conversation, with the talking circuit exactly as stated at the end of the preceding paragraph.

Called line busy If the called line is busy, its test conductor, 

